One of the most pressing challenges in water purification is the removal of per- and polyfluoroalkyl substances (PFAS) - a large class of toxic, persistent pollutants originating from aviation firefighting foams and industrial surfactants. Human exposure to PFAS represents a significant global health and economic burden, with even low concentrations in blood linked to cancer and several chronic diseases. Current adsorbent materials struggle to remove PFAS efficiently due to slow adsorption kinetics and particularly poor affinity for short-chain PFAS. A molecular-level understanding of PFAS capture is therefore needed to guide the design of next-generation adsorbents.
In this talk, I present our recent work using water-soluble coordination cages based on Fujita’s PdII octahedron to trap PFAS, including short-chain variants.[1] Host-guest studies in water reveal that the cage binds C4–C8 PFAS with high affinity (log K ≈ 5) through a cooperative mechanism where aggregates of anionic PFAS species are bound within the cavity simultaneously. By implementing rigid cis-capping ligands into the cage structure, we also develop hosts with smaller cavities, capable of binding highly water-soluble C3 PFAS, which typically cannot be bound effectively by other larger cages.
We translate this host-guest chemistry into a functional material by encapsulating the PdII-based cages within mesoporous silica to create a “host-in-host” adsorbent. While the silica alone shows no PFAS affinity, incorporation of just 1 wt% cage enables >98% removal of a broad range of PFAS under flow-through filtration. The adsorption capacity correlates with host–guest chemistry, and regeneration of the material is demonstrated over five cycles.